The invention relates to a frequency converter for the assembly on an electric motor.
It is nowadays counted as belonging to the state of the art, to arrange a frequency converter or frequency transformer, as is applied with modern motors for the control of the rotation speed, in particular for achieving rotation speeds beyond the rotation speed which is physically inherent of the mains frequency, in a housing which is designed and envisaged for assembly on the electric motor, so that the frequency converter and the motor may be wired to one another in a fixed manner, and may be handled and installed together. The frequency converter housing thereby is typically designed in the manner of an enlarged terminal box and is arranged at a certain distance on the outer periphery of the motor. The frequency converter housing, in particular the lower housing part connected to the motor, is heat-conducting, typically of metal and designed in a ribbed manner, in order to lead away the heat which occurs particularly in the power circuit, but also in the remaining frequency converter. Thereby, it is counted as belonging to the state of the art, to arrange cooling ribs on the lower side of the frequency converter housing, which lie in the cooling air flow of the motor, said air flow being produced by a fan seated on one end of the motor shaft, and a fan cowl arranged surrounding this fan at the end-side of the motor, and flowing along the outer side of the motor on the peripheral side and thus hits the lower side of the frequency converter housing and the cooling ribs which are provided there.
This cooling principle, although having proven its worth, it is somewhat problematic with regard to the design, to suggest as compact as possible, design of the frequency converter, but on the other hand to select the cooling and arrangement of the components such that different heat zones are arranged, in accordance with the thermal load characteristics of the individual components. Thus for example, the electronic switches of the power circuit as a rule may withstand higher operating temperatures than the capacitors of the intermediate circuit, and these in turn may withstand higher temperatures than the control and regulation electronics.